Cylindrical filters and their manufacture

ABSTRACT

A cylindrical filter is formed from a sheet of filter material which includes two connected layers of filter media. Opposed edges of the sheet are joined to form the cylinder by separating the media adjacent the edges and then sealing together the first of the separated layers followed by sealing the second of the separated layers. The two seals are spaced inwardly of the edges and are spaced from one another. In this way, failure of one seal does not result in failure of the cylindrical filter.

This application is a divisional of application Ser. No. 07/642,652,filed Jan. 17, 1991, now U.S. Pat. No. 5,185,190.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The invention relates to cylindrical filters and their manufacture.

A cylindrical filter is customarily formed from a sheet of filter mediajoined along two opposed edges to form the cylinder. The media may be inthe form of a plain sheet or the sheet may be corrugated, in which casethe joined edges are the final corrugations.

2. Brief Review of the Prior Art

The joint is customarily made by contacting the areas of the sheetadjacent The two edges and then forming a seal between these areas. Ingeneral, the overlap will be with the edges in register, particularlywhere the sheet is pleated. Such a sealed joint is acceptable where thesheet is formed from a single layer of filter media. It is, however,less satisfactory where the sheet is formed from two superimposed layersof media connected together. In this case, the possibility of a flowpath through a single seal is increased.

In EP-A1-0001407 there is disclosed the joining of the edges of a sheetformed of two superimposed layers of media connected together andutilizing a channel strip for connecting the layers of media together.In U.S. Pat. No. 3,865,919 a number of corrugations of a pleated sheetof filter material are bonded together and then provided with a tape orribbon of adhesive in a space formed between the corrugations. Theadhesive is melted to form a leak-proof seal.

SUMMARY OF THE INVENTION

According to the first aspect of the invention, there is provided amethod of forming a filter from a sheet of filter material including twolayers of filter media by joining two opposed edges of the sheet to forma cylinder, the method comprising separating the filter media from saidopposed edges to form two separate layers, contacting a first layer atone edge with a first layer at the other edge, sealing said contactinglayers together with said seal extending along the length of said edgesat a position spaced inwardly of said edges, positioning the secondlayer of said one edge and the second layer of said other edge so thatsaid second layers at least partially overlie the sealed first layers,and then forming a seal between said second layers to each other, withsaid second seal extending along the length of said edges at a positioninwardly of said edges and spaced from said first mentioned seal.

In this way, two separate seals are provided, which means that a failureof one seal need not result in a flow path between the edges.

According to a second aspect of the invention, there is provided acylindrical filter formed from a sheet of filter material and includingtwo connected layers of filter media, two opposed edges of the sheetbeing joined to form said cylinder, the layers being separated alongsaid edges, a first layer of one edge being sealed to a first layer ofthe other edge along the length of the edges by a first seal spacedinwardly of said edges and a second layer of said one edge being sealedto a second layer of the other edge along the length of said edges by asecond seal spaced inwardly of said edges and spaced from said firstmentioned seal.

The following is a more detailed description of some embodiments of theinvention, by way of example, reference being made to the accompanyingdrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of part of a cylindrical pleated filterformed from a sheet of filter material including two connected layers offilter media and joined at the final corrugations,

FIG. 2 is a diagrammatic view of a holder holding the ends of thepleated sheet shown in FIG. 1 before joining and showing a first stagein the joining process,

FIG. 3 is a similar view to FIG. 2, but showing a second stage in thejoining process,

FIG. 4 is a similar view to FIG. 1, but showing a second form of joinbetween the final corrugations,

FIG. 5 is a similar view to FIG. 1 but showing a sheet of filter mediaformed from three connected layers of media and three seals, the sealsconnecting two, four and six layers of media respectively,

FIG. 6 is a similar view to FIG. 4 but showing a sheet of filter mediaformed from three connected layers of media and three seals, each sealconnecting two of the layers,

FIG. 7 is a similar view to FIG. 5 but showing only two seals, one sealconnecting two layers and the other seal connecting all six layers, and

FIG. 8 is a similar view to FIG. 6 but showing only two seals, one sealconnecting two layers and the other seal connecting the remaining fourlayers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the cylindrical filter is formed from a sheetof filter material having two layers of filter media 10, 11 whichoverlie one another add which are connected to one another. These layers10, 11 are covered by upstream and downstream drainage material 12, 13.The layers of filter media are of nylon.

The sheet is corrugated to form two final corrugations 14, 15, whichboth extend in the same direction and terminate at respective edges 16,17.

The sheet is formed into a cylinder in the following way.

First, the downstream drainage material 13 is removed from the firstmedia layer 10 inwardly of the edges 16, 17 and along the length of theedges 16, 17. The first and second media layers 10, 11 and the upstreamdrainage material 12 are then separated at the edges 16, 17 for thecomplete height of the final corrugations 14, 15 and along the completelength of the final corrugations 14, 15 to form three separate layers,each of the filter media layers 10, 11 having its respective edges 16a,17a, 16b, 17b.

The corrugated sheet with the separated layers is then mounted in theholder shown in FIG. 2. This holder comprises a member 18 of T-shapedcross-section with the head 19 of the T movable so that the edges 20 ofthe head can engage with and disengage from respective supports 21. Thewidth of the head is generally equal to twice the height of thecorrugation of the completed sheet with which it is designed to be used.

The penultimate folds 22 of the sheet, prepared as described above, arearranged around the edges 20 of the head 19 of the member 18 and engagedwith the supports 21. This ensures that the two edges 16, 17 areparallel.

The two separated first layers 10 are then brought together by manualmanipulation, as seen in FIG. 2. As shown in FIG. 3, the edges 16a, 17aof the first layer 10 are in register. These layers are then sealedtogether between heated jaws to form a seal extending parallel to theedges 16a, 17a and inwardly of the edges. The position and width of thisseal are designated by the letter A in FIG. 1 and it will be seen thatthe seal is adjacent the final folds 23, 24 of the pleated sheet.

Referring next to FIG. 3, the second layers are then positioned manuallyto overlie the joined first layers 10 so that the edges 16b, 17b of thesecond layer 11 as well as the edges 16a, 17a of the first layer 10 areall in register, as shown in FIG. 1. The layers 10, 11 are then placedwithin jaws which form a second seal extending inwardly of the edges 16,17 parallel to said edges and spaced from the first seal A. This sealconnects together all of the layers. The width and position of this sealare indicated by the letter B in FIG. 1 and it will be seen that thisseal is between the first seal A and the edges 16, 17.

Finally, the upstream drainage material 12 is re-assembled over thesecond layers 11.

There is thus formed a pleated cylindrical filter in which the finalcorrugations are joined inwardly of their edges by two parallel butspaced seals A, B. If the seal B should fail in its central portion, theseal A will still remain. If the seal B should fail towards its outeredges, leaking material will still have to pass through the filtermedia. In addition, longitudinal strength is increased and there is anincrease of strength in a cartridge in which the corrugated filter isincorporated.

Six pleated cylindrical filters prepared as described above withreference to the drawings were tested in the following way.

All six cartridges were placed in an autoclave at 140° C. for fourperiods of one hour each. All six cartridges were tested for forwardflow before the four one hour cycles and after the four one hour cycles.The filters were tested water wet at 2.61 kPa (18 psi).

An acceptable production limit for such forward flow is 10 ml/min and anacceptable limit in use is 22 ml/min.

The results were as follows:

    ______________________________________                                        FORWARD FLOW IN MLS/MIN                                                       Filter No   Before Steaming                                                                            After Steaming                                       ______________________________________                                        1           1.97         1.30                                                 2           2.05         1.60                                                 3           2.13         1.00                                                 4           2.07         1.36                                                 5           2.17         1.18                                                 6           1.93         1.25                                                 ______________________________________                                    

It will thus be seen that all filters remain well within the acceptablelimits after autoclaving. This indicates that there has been no failureof the seals.

It will be appreciated that the method of manufacture and constructiondescribed above need not be applied to pleated filters, it could beapplied to filters in which no pleats are provided. Further, the joinmay not be with the two edges in register, it could be with the twoedges overlapping.

A second form of join is shown in FIG. 4. Aspects of this join and thejoin described above with reference to FIGS. 1 to 3 are the same andthese aspects will not be described in detail.

In this second form of join, the first seal A is formed as describedabove with reference to FIGS. 1 to 3. However, after formation of thisseal A, the regions of the first media layer 10 between the seal A andthe edges 16b, 17b of the second media layer 11 are cut-away. As shownin FIG. 4, the edges 16a, 17a of the first layer 10 are in register andare spaced from the edges 16b, 17b of the second layer 11, which arealso in register.

Thus, when the second media layers 11 are positioned as shown in FIG. 3,these layers 11 only partially overlie the first media layers 10 andportions of the second media layers 11 are in contact. The second seal Bis formed between these contacting second media layer portions 11, asshown in FIG. 4.

The upstream drainage material 12 is then re-assembled. It will beappreciated that filters having three or more media layers may be joinedby either of the methods described above with reference to the drawings.In such cases, the media layers may all be separated and joinedsuccessively in pairs by spaced seals, so that there are as many sealsas layers. This is shown in FIGS. 5 and 6 where parts common to FIGS. 1and 4 and to FIGS. 5 and 6 will be given the same reference numerals andwill not be described in detail. In these embodiments, the cylindricalfilter is formed from a sheet of filter material having three layers offilter media 10, 11, 25 which overlie one another and are connected toone another. The layers of filter media 10, 11, 25 are of nylon.

The sheet is corrugated to form two final corrugations 14, 15, whichboth extend in the same direction and terminate at respective edges 16,17.

The sheet of FIG. 5 is formed into a cylinder in the way described abovewith reference to FIG. 1 except that the third media layer 25 is alsoseparated at the edges 16, 17 for the complete height of the finalcorrugations 14, 15 and along the complete length of the finalcorrugations 14, 15 to form six separate layers.

The layers 10, 11 are joined as described above with reference to thedrawings. The portions of the separated third layer 25 are then broughttogether by manual manipulation. As shown in FIG. 5, both edges 16a,17a, 16b, 17b, 16c, 17c of all of the filter media layers 10, 11, 25 arein register. The layers are then sealed together between heated jaws toform a seal extending parallel to the edges 16, 17 and inwardly of theedges. The position and width of this seal are designated by the letterC in FIG. 5 and it will be seen that the seal is adjacent the finalfolds, and closer to the edges 16, 17 than the previously formed sealsA, B.

Finally, the upstream drainage material 12 is re-assembled over thesecond layers 11.

There is thus formed a pleated cylindrical filter in which the finalcorrugations are joined inwardly of their edges by three parallel butspaced seals A, B, C. If the seal C should fail in its central portion,the seals A and B will still remain. If the seal C should fail towardsits outer edges, leaking material will still have to pass through thefilter media. In addition, longitudinal strength is increased and thereis an increase of strength in a cartridge in which the corrugated filteris incorporated.

The second form of join is shown in FIG. 6. Aspects of this join and thejoin described above with reference to FIGS. 1 to 5 are the same andthese aspects will not be described in detail.

In this second form of join, the first seal A and the second seal B areformed as described above with reference to FIG. 4. However, afterformation of the second seal B, the portions of the second media layer11 between the seal B and the edges 16c, 17c of the third media layer 25are cut-away. As shown in FIG. 6, the edges 16b, 17b of the second layer11 are in register and are spaced from the edges 16c, 17c of the thirdlayer 25, which are also in register.

Thus, when the portion of the third media layer 25 are positioned asshown in FIG. 6, these portions only partially overlie the first andsecond media layers 10, 11 and are in contact. The third seal C isformed between these contacting third media layer portions 25, as shownin FIG. 6.

Alternatively, two layers (or more where there are four or more layers)near each edge may be joined together so that there are less seals thanlayers. This is shown in FIGS. 7 and 8 where parts common to FIGS. 1 to6 and to FIGS. 7 and 8 will be given the same reference numerals andwill not be described in detail.

In FIG. 7, the third media layer 25 is not separated from the secondmedia layer 11 and the portions near the edges 16b, 17b, 16c, 17c 16, 17of these two layers 11, 25 are sealed together as one, as describedabove with reference to FIGS. 2 and 3. There are thus only two seals A,B, with the same seal A connecting two portions of the first media layer10, and the other seal B connecting all six portions of all of the medialayers 10, 11, 25.

In FIG. 8, the third media layer 25 is not separated from the secondmedia layer 11 and the portions near the edges 16b, 17b, 16c, 17c ofthese two layers are sealed together as one, as described above withreference to FIG. 4. There are only two seals A, B with the inner sealconnecting the two portions of the first media layer 10, and the outerseal connecting the four portions of the remaining media layers 11, 25.

What is claimed is:
 1. A method of forming a filter from a sheet of filter material including at least first and second layers of filter media, each layer having first and second edges, comprising the steps of:(a) contacting a portion of the first layer of filter media near the first edge with a portion of the first layer near the second edge; (b) sealing the contacting portions together with a first seal with the first seal extending along the length of the edges at a first position spaced from the edges, without a seal at the edges; (c) positioning a portion of the second layer of filter media near the first edge of the first layer and a portion of the second layer near the second edge of the first layer so that the second layer portions at least partially overlie the sealed first layer portions; and then (d) forming a second seal between the second layer portions, with the second seal extending along the length of the edges at a second position spaced from the edges, without a seal at the edges, and spaced from the first seal.
 2. The method according to claim 1 wherein contacting portion of the first layer includes placing the respective edges thereof in register, wherein the first layer is sealed together and then the second layer is sealed with the second seal.
 3. The method according to claim 2 wherein positioning the second layer portions includes contacting the portions of the second layer and wherein forming a seal between the second layer portions includes forming a seal between the contacting second layer portions.
 4. The method according to claim 2 wherein when the second layer is positioned to at least partially overlie the first layer, the edges of the first and second layers are in register, so that the second seal seals together the first and second layers.
 5. The method according to claim 3 wherein the sheet is corrugated with the seals being formed between final corrugations of the sheet, the first seal being between downstream filter media and the second seal being between upstream filter media.
 6. The method according to claim 1 wherein the sheet is provided with a surface drainage material on both surfaces thereof, the method including removing the drainage materials from the edges before sealing.
 7. The method according to claim 1 wherein the sheet of filter material has at least three layers of filter media, at least one of the layers additional to the first and second layers being maintained connected to the first or second layer during the method.
 8. The method according to claim 1 wherein the sheet of filter material further includes a third layer having first and second edges and where the method further comprises positioning a portion of the third layer near the first edge and a portion of the third layer near the second edge so that the third layer portions at least partially overlie the sealed first and second layer portions; and forming a seal between the third layer portions, with the third seal extending along the length of the edges at a position spaced from the edges and spaced from the first and second seals.
 9. The method according to claim 3 further comprising removing part of the first layer portions beyond the first seal after the first layer portions are sealed together.
 10. A method according to claim 1 wherein sealing the first layer portions further comprises sealing the first layer portions with the first and second edges of the first layer extending in the same direction from the first seal.
 11. A method according to claim 10 wherein sealing the second layer portions further comprises sealing the second layer portions with the first and second edges of the second layer extending in the same direction from the second seal.
 12. A method according to claim 1 wherein sealing the second layer portions further comprises sealing the second layer portions with the first and second edges of the second layer extending in the same direction from the second seal.
 13. A method according to claim 8 wherein sealing the first layer portions further comprises sealing the first layer portions with the first and second edges of the first layer extending in the same direction from the first seal.
 14. A method according to claim 8 wherein sealing the second layer portions further comprises sealing the second layer portions with the first and second edges of the second layer extending in the same direction from the second seal.
 15. A method according to claim 14 wherein sealing the third layer portions further comprises sealing the third layer portions with the first and second edges of the third layer extending in the same direction from the third seal.
 16. A method according to claim 13 wherein sealing the third layer portions further comprises sealing the third layer portions with the first and second edges of the third layer extending in the same direction from the third seal.
 17. A method according to claim 8 wherein sealing the third layer portions further comprises sealing the third layer portions with the first and second edges of the third layer extending in the same direction from the third seal.
 18. A method of forming a filter from at least first and second adjacent layers of filter media, each adjacent layer having first and second edges, comprising the steps of:(a) sealing a first portion of a first layer of filter media with a second portion of the first layer using a first seal extending only along the length of the first and second edges of the first layer at a first position, wherein the first and second edges of the first layer extend in the same direction from the first seal; (b) sealing a first portion of the second layer of filter media with a second portion of the second layer of filter media using a second seal extending only along the length of the first and second edges of the second layer of filter media at a second position spaced from the first seal, wherein the first and second edges of the second layer extend in the same direction from the second seal.
 19. The method according to claim 18 wherein sealing includes sealing the first layer with the first and second edges of the first layer in register and sealing the second layer with the first and second edges of the second layer in register.
 20. The method according to claim 19 wherein sealing includes sealing the first and second layers with the first and second edges of the first layer spaced from the first and second edges of the second layer.
 21. A method of forming a filter from at least first and second adjacent layers of filter media, each adjacent layer having first and second edges, comprising the steps of:(a) sealing a first portion of the first layer of filter media near the first edge with a second portion of the first layer near the second edge using a first seal extending only along the length of the first and second edges of the first layer at a first position spaced from the first and second edges of the first layer, wherein the first and second edges of the first layer are in register and extend in the same direction from the first seal; (b) sealing a first portion of the second layer of filter media near the first edge with a second portion of the second layer near the second edge using a second seal extending only along the length of the first and second edges of the second layer at a second position spaced from the first seal and from the first and second edges of the second layer, wherein the first and second seals are adjacent to each other, the first and second edges of the second layer are in register, and wherein the first and second edges of the second layer extend in the same direction from the second seal.
 22. A method according to claim 21 wherein sealing includes sealing the first and second layers of filter media with the first and second edges of the first layer spaced from the first and second edges of the second layer. 